1. Field of the Invention
This invention relates to a rotary head type recording and reproducing apparatus and more particularly to an apparatus arranged to record main information signals on a tape-shaped recording medium by forming many parallel recording tracks with an additional information signal recorded solely at a predetermined part of each of the recording tracks; and to reproduce these recorded signals by means of rotary heads.
2. Description of the Prior Art
In this specification, among the apparatuses of the kind mentioned above, audio tape recorders arranged to record audio signals as main information signals by time-base compressing them and by digitally modulating them with rotary heads are taken up by way of example in describing this invention.
FIG. 1 of the accompanying drawings shows by way of example the tape transport system employed in the audio tape recorder of the above-stated kind. The illustration includes a magnetic tape 1; a rotary cylinder 2 which carries a pair of rotary heads 3 and 4. The heads 3 and 4 are thus arranged to obliquely trace the surface of the tape 1 in recording an audio signal on the tape. An audio signal tape recorder capable of exclusively recording audio signals in a total of six channels can be obtained by arranging it to record a time-base compressed audio signal in each of six areas formed on the tape 1 in the longitudinal direction thereof every time these heads 3 and 4 rotate 36 degrees.
The following briefly describes this tape recorder:
FIG. 1 shows the tape transport system of the above-stated tape recorder. FIG. 2 shows recording tracks formed on a tape by this tape recorder. While the head 3 or 4 traces distances from a point A to a point B, from the point B to a point C, from the point C to a point D, from the point D to a point E, from the point E to a point F and from the point F to another point G, audio signals can be recorded in areas CH1 to CH6. These areas CH1 to CH6 thus can be used for recording different audio signals therein respectively. An operation called azimuth-overwite is performed on these areas. However, the tracks of these areas CH1-CH6 do not have to be on the same straight line. Each of the areas CH1-CH6 has one pilot signal recorded therein for tracking control. Different pilot signals are thus recorded in different areas in the order of rotation f1.fwdarw.f2.fwdarw.f3.fwdarw.f4. However, there is no correlation between them.
Referring further to FIG. 1, recording or reproduction is carried out in or from these areas CH1 to CH3 while the tape 1 is travelling at a predetermined speed in the direction of arrow 7 and in or from the areas CH4 to CH6 while the tape is travelling in the direction of arrow 9. Therefore, as shown in FIG. 2, the inclination of the areas CH1 to CH3 somewhat differs from that of the areas CH4 to CH6. With regard to a difference in the relative speed of the tape and the head for these groups of areas, a difference arising from the travel of the tape 1 is extremely small as compared with a difference arising from the rotation of the heads 3 and 4. Therefore, the difference in the relative speed presents no problem.
FIGS. 3(a) to 3(j) show in a time chart the recording or reproducing operation of the tape recorder which is arranged as described above. A phase detection pulse (hereinafter referred to as a PG signal) which is generated in synchronism with the rotation of the cylinder 2 as shown at FIG. 3(a). The PG signal is of a rectangular wave of 30 Hz repeating a high level (hereinafter referred to as an H level) and a low level (hereinafter referred to as an L level) alternately with each other at intervals of 1/60 sec. Another PG signal which is of the opposite polarity to the PG signal of FIG. 3(a) is shown in FIG. 3(b). The first PG signal is at an H level while the head 3 is rotating from the point B to the point G of FIG. 1. The other PG signal shown in FIG. 3(b) is at an H level while the other head 4 is rotating from the point B to the point G.
Pulses for reading data are obtained from the PG signal of FIG. 3(a) as shown in FIG. 3(c). The data reading pulses are used for sampling the audio signal of a period corresponding to one field (1/60 sec). FIG. 3(d) shows by H level parts thereof periods provided for signal processing on the one field portion of the sampled audio data by adding an error correcting redundant code or by changing the arrangement thereof by means of a RAM or the like. FIG. 3(e) shows a signal indicating data recording periods at H level parts thereof which represent timing for recording, on the tape 1, the recording data obtained through the signal processing operation mentioned above.
Referring to FIGS. 3(a) to 3(j), the temporal flow of signals are, for example, as follows: The data sampled during a period from a point of time t1 to a point of time t3, i.e. while the head 3 is moving from the point B to the point G, is subjected to a signal processing operation during a period from the point of time t3 to a point of time t5, i.e. while the head 3 is moving from the point G to the point A and are then recorded during a period from the point of time t5 to a point of time t6, or while the head 3 is moving from the point A to the point B. In other words, the data is recorded by the head 3 in the area CH1 as shown in FIG. 2. Meanwhile, the data which is sampled while the PG signal of FIG. 3(b) is at an H level is also processed at a similar timing before it is recorded in the area CH1 by the head 4.
FIG. 3(f) shows another PG signal which is obtained by shifting the phase of the PG signal of FIG. 3(a) to a predetermined degree, which corresponds to one area and is 36 degrees in this specific instance.
An audio signal recording operation using the PG signal of FIG. 3(f) and a PG signal which is not shown but is of an opposite polarity to the former is performed in the following manner: The data which is sampled during a period between the points of time t2 and t4 is subjected to a signal processing operation during a period between the points of time t4 and t6 in accordance with the signal of FIG. 3(g) and is recorded during a period between the points of time t6 and t7 in accordance with the signal of FIG. 3(h). In other words, the data is recorded in the area CH2 of FIG. 2 while the head is moving from the point B to the point C. Meanwhile, another data which is sampled during the points of time t4 and t7 is likewise recorded in the area CH2 by means of the other head during a period between the points of time t4 and t7.
The signal which is recorded in the area CH2 in the manner as described above is reproduced in the following manner:
The head 3 reads the data from the tape 1 in accordance with a signal shown in FIG. 3(h) during the period between the points of time t6 and t7 (and also during the period between the points of time t1 and t2). Then, during the period between the points of time t7 and t8 also (between t2 and t3), the reproduced signal is subjected to a signal processing operation which is carried out, in a manner reverse to the signal processing operation performed for recording, in accordance with a signal shown in FIG. 3(i). In other words, error correction and other processes are carried out during this period. Then, during a period between points of time t8 and t9, the reproduced audio signal which has been thus processed is produced in accordance with a signal shown in FIG. 3(j). The reproducing operation of the head 4 is of course performed with a phase difference of 180 degrees from the above-stated reproduction by the head 3, so that a continuous reproduced audio signal can be obtained.
For other areas CH3 to CH6, it goes without saying that the recording and reproducing operations are performed on the basis of the PG signal of FIG. 3(a) by phase shifting it as much as n.times.36 degrees. This is independent of the travelling direction of the tape.
The tape recorder of the type operating in the manner as described above can be readily arranged to be capable of recording audio signals for a length of time of, for example, 90 minutes in each area and thus can be arranged to perform audio signal recording over such a long period as nine hours. This, however, brings about a problem on the part of the operator that an excessively long period of time becomes necessary in searching out a desired part of the record on the tape. It is conceivable to solve this problem by having indexing data generated and recorded as an auxiliary information signal in recording data corresponding to the audio signal.
However, the searching efficiency cannot be increased if the indexing data are used by reproducing them at the same tape travel speed as the speed employed for recording. Meanwhile, an increased travelling speed of the tape would make it difficult to reproduce the indexing data recorded.
Further, during recent years, rotary head type recording apparatuses such as video tape recorders (hereinafter referred to as VTR) and digital audio tape recorders (hereinafter referred to as DAT) have come to be arranged to perform recording with further increased recording density. As a result of this trend, some of these apparatuses have come to record signals with recording tracks arranged to be formable at a plurality of different track pitches. In the apparatuses of this kind, the recording track pitch (hereinafter referred to as TP for short) is normally determined by the travelling speed of the recording medium at which recording is performed. In the case of a VTR, for example, the recording travelling speed of the tape is arranged to be variable between a larger track pitch recording/reproducing speed (called a standard mode speed which hereinafter will be referred to simply as the SP mode) and a smaller track pitch recording/reproducing speed (called a long time mode speed which hereinafter will be referred to simply as the LP mode). The SP mode speed is faster than the LP mode speed by about 2 to 3 times.
At the time of reproduction of the record, the apparatuses of this kind necessitates making a discrimination between the SP and LP mode recording speeds. For this purpose, the conventional VTR is arranged to form a control track which extends in the longitudinal direction of the tape with a control signal of a given frequency recorded in this track. Then, at the time of reproduction, this control signal is reproduced to make a discrimination between the SP and LP modes according to the frequency of the control signal reproduced. However, it is a short-coming of the apparatus of this kind that the additional track separately formed in the longitudinal direction of the tape hinders efforts to further increase the recording density. This shortcoming presents a serious problem especially in the case of the apparatus arranged to perform recording and reproduction by longitudinally forming a plurality of areas along a tape-shaped recording medium, because, in that instance, the longitudinal, separately formed recording track must be formed also in a plural number which is hardly practicable.
Another method has been contrived for making a discrimination between the SP and LP modes by utilizing a signal recorded in a helical recording track in which an information signal is recorded. For example, tracking control pilot signals (hereinafter referred to as TPS's) which are reproduced are used for this purpose. The TPS's are, for example, recorded in a manner called the four frequency method. According to the conventional method, the discrimination between the SP and LP modes is made either by detecting how many different frequencies of these TPS's have been reproduced in a certain given period of time or by detecting the frequency of a tracking error signal obtained from the reproduced TPS's. However, it is difficult to apply this method to an apparatus of the kind which forms a plurality of areas extending in the longitudinal direction of a tape-shaped recording medium and performs recording and reproduction in and from each of these longitudinal areas, because: The reproducible level of the TPS is not so high. Besides, the recording track pitch of one of these areas might differ from that of another area. This necessitates sampling for each of the areas. These factors thus present a problem for detection by means of the TPS's. Even if this problem can be solved, in the event of an apparatus of the type permitting selection of more than three different recording track pitches, a discrimination of one track pitch from another not only necessitates an extremely complex circuit arrangement but also is very difficult. Therefore, such a method is hardly applicable to the apparatus of that type.